Survival factors suppress apoptosis by activating the
serine/threonine kinase Akt. To investigate the molecular mechanism underlying activated Akt's ability to protect neurons from
hypoxia or
nitric oxide (NO) toxicity, we focused on the apoptosis-related functions of p53 and
caspases. We eliminated p53 by employing p53-deficient neurons and increased p53 by
infection with recombinant adenovirus capable of transducing p53 expression, and we now show that p53 is implicated in the apoptosis induced by
hypoxia or NO treatments of primary cultured hippocampal neurons. Although
hypoxia and NO induced p53, treatment with
insulin-like growth factor-1 significantly inhibited caspase-3-like activation, neuronal death and transcriptional activity of p53. These
insulin-like growth factor-1 effects are prevented by
wortmannin, a
phosphatidylinositol 3-kinase inhibitor. Adenovirus-mediated expression of activated-Akt
kinase suppressed p53-dependent transcriptional activation of responsive genes such as Bax, suppressed caspase-3-like
protease activity and suppressed neuronal cell death with no effect on the cellular accumulation and nuclear translocation of p53. In contrast, overexpression of
kinase-defective Akt failed to suppress these same activities. These results suggest a mechanism where Akt
kinase activation reduces p53's transcriptional activity that ultimately rescues neurons from
hypoxia- or NO-mediated cell death.